Capillary wave propagation on solutions of surfactants: a new method for kinetic studies

Abstract

It is well-known that adsorption kinetics influences the damping coefficient of capillary waves. However, only a few kinetics studies of adsorption based on this effect have been published in the literature. We show that the method of low-frequency capillary waves has certain advantages as compared with other methods traditionally used for this purpose. It can be applied also to the investigation of the micellization kinetics.

The damping coefficient and the wavelength of ripples on the surface of aqueous solutions of sodium dodecylsulfate (SDS) and dodecylpyridinium bromide (DPB) have been measured as a function of surfactant concentration. For both systems are adsorption at the airwater interface is essentially diffusion controlled. Above the Critical micelle concentration (CMC) a slight increase of the damping for solutions of SDS is connected with a corresponding change of the shear viscosity of the bulk phase. For DPB solutions the results can be explained only if the micellization kinetics are taken into account. The estimated values of the relaxation time for the slow stage of the micellization process are in agreement with the results obtained in the course of investigations of bulk phases.